Method of treating cellulosic textile material



Fatented Jan. 36 i945 MIE'EHOD OF TREATING CELLULOSIC TEXTILE MATERIALEric Owen Rldgway, Upper Montciair, and Frederick Curtis Tucker andCharles J. Kintner,

Nutley, N. 3., assignors to Bidbo Laboratories, linc., a corporation ofNew Jersey No Drawing. Application August 28, 1940, Serial No. 354,582

8 Claims.

This invention relates to the treatment of cellulosic textile materialsuch as cotton, jute, linen and the like, preferably in the form ofthread, yarn or woven material.

Among the primary objects of the invention is the chemical and physicaltreatment of cellulosic fibres which is relatively inexpensive,efiective and easily controllable and adapted to produce a more readilyabsorbent and stronger textile fibre of substantially pure alphacellulose from which the impurities have in large part been removed.-The treatment greatly increase the tensile strength of the celiulosicmaterial, to an extent far greater than that which would be expected byone skilled in the art; the tensile strength being increasedapproximately 20% and over above untreated gray goods and abovegoodstreated according to the well-known mill methods of kiering,bleaching and mercerizing,'or combinations thereof.

The improved method of treatment has the added advantage of beingapplicable to any continuous process of treating cellulosic material,such as mercerization,bleaching, or both; because our method ispreferably carried out continuously.

The improved method comprises primarily two steps; the first step may betermed a conditioning step in that it partially removes impuritiespresent in the cellulosic fibres, such as waxes, pectins and the lessercelluloses, and leaves the cellulosic textile material in the desiredstate for the second step of the method. The second step of the improvedmethod comprises a combination of chemical and physical action on thecellulosic material, and it is during this step that the majorproportion of the improvement in' tensile strength, appearance andabsorbency is obtained.

The first or conditioning" step of the improved method-can bepartiallyperformed by' any of the well-known methods of kier boilin or bleachingor combinations thereof. Howeve we prefer to treat the cellulosictextile material in relatively high concentrations of sodium hydroxideor ,po-

'tassium hydroxide since we hav 'found thatlthis treatment is superiorto the normal kier boil and can be completed in a relatively short time.After this treatment the materials are thoroughly washed in water toremove the hydroxide-and are then ready for the second step of theprocess. which broadly comprises a plurality of immersions in a dilutewater-solubleacid such as dilute sulphuric acid. Before the first bathand after each immersion thematerial is subjected to a mechanicalsqueezing action such as being forced through squeeze rolls.

In the first or conditioning step, the boiling sodium hydroxidepreferably ranges in concentration from 12 to 96 grams sodium hydroxideper litre, and the material may be immersed in this solution at aboiling temperature for a period of from three minutes to two hourswithout deleterious action on the cellulosic fibres or any ap-.preciably greater loss in weight, length or size of the yarn and threadthan is now obtained in the well-known mill methods, although asmentioned the more dilute kierboiling concentration may be employed withsomewhat less satisfactory results. In commercial operations, the periodof immersion in the boiling sodium hydroxide solution may be tenminutes, since further immersion produces improvements generally sosmall as not to be commercially feasible, except in such instances aswhen the material is so tightly packed in the vessel that thecirculation of the solution is impaired and in such instances longerperiods of immersion are desirable, although it is to be understood thatlonger immersion periods up to the limits expressed do not deleteriouslyaffect the material being treated.

This first step in our'improved method does not require the use ofspecial equipment since it is not necessary that the material be treatedunder pressure unless a slight pressure is necessary to obtain thoroughcirculation of the treating solution throughout the material. Forexample, a kier,

open tank or a Hussong machine may be employed; an injector type ofkier, in which the solution is heated by live steam and circulated, has

, been satisfactorily employed since if the solution is at the boilingtemperatures when the material is immersed, dilution caused by the steamis not appreciable.

The final stage in the first step of the method comprises washing thecellulosic material, preferably cotton, until substantially free ofchemicals employed and the dissolvedor partially dissolved impurities.It is preferred to wash the material major improvement in tensilestrength, appearance and absorbency is obtained.

The material is subjected to a plurality of treatments in a dilutesolution of a water-soluble acid, organic or inorganic, or acid salt,preferably at room temperature. For example, sulphuric acid has beensatisfactorily employed at concentrations varying from 3 grams to 70grams per litre, and a typical satisfactory solution is that employing38 grams per litre sulphuric acid. Before the first bath and betweeneach succeeding bath, the material is passed through mechanical squeezerolls which are set to obtain a 70% moisture retention, or lower, andmay be preferably maintained to secure approximately 50% retention orlower. A thorough squeeze of the material, such as obtained by themoisture retentions indicated, i quite important to obtain the desiredresult. The cellulosic material need only be immersed in the acidsolution long enough to completely saturate all of the fibres, althoughthe time may be varied depending upon whether the material being treatedis in the form of cloth, yarn, thread or fibres; there is no deleteriouseffect on the material over a relatively longer period of immersion aslong as the material is completely submerged in the solution. Theconcentration of the acid bath may be increased slightly with eachsucceeding bath.

As previously mentioned, the squeeze rolls should be set to give'aresidual moisture retention of less than 70% of the weight of the drycellulosic material being treated, and to obtain the best results it isessential that the residual moisture retention should be 50% or under.The importance of the tightness of the mechanical squeeze rolls throughwhich the cellulosic material is run before and after aturation in aplurality of dilute acid baths, is illustrated by the improvementobtained in cotton thread so treated. It has been found that where thesqueeze rolls are set to give over 70% retention of the solution in thefibres, practically no increase in tensile strength is obtained, whereasup to and beyond 20% tensile trength improvement is obtained when thesqueeze rolls are set so that the solution retention in the fibres islowered below 70%. Accordingly, it will be understood that while thepretreatment of the textile material may be varied as previously setforth, and while various water-soluble acids and concentrations thereofmay be employed to obtain satisfactory results, it is essential that thematerial be squeezed to the extent indicated before the first bath andafter each immersion in the acid bath.

The number of acid baths preferably ranges from four to ten and, formost materials, the desired results are obtained after a total of sevensqueezes and six immersions in the acid solution. For example, with thisnumber of physical and chemical treatments, it has been found that thetensile strength of the material is increased approximately 20%. Someimprovement has been obtained by the use of two acid baths, the materialbeing squeezed in the manner mentioned before, between and after thebaths. However, since it has been found that the tensile strengthincreases with a greater number of consecutive acid baths with squeezesbetween each bath and after the final bath, a greater number ofconsecutive acid baths is preferred. The improvement after tenconsecutive baths and eleven squeezes of the type described is not ofgreat importance, although there is some purification of the fibrousstructure up to ten baths.

The acid and squeezing treatment may be performed with relatively simpleapparatus, for example, a single acid chamber may be employed over whichare mounted seven sets of squeeze rolls of the type described soarranged that the cellulosic textile material will receive sixsaturations in the dilute acid solution with a mechanical squeeze of thenature described before the first immersion and between each subsequentimmersion and after the final bath. The use of a centrifuge or otherdrying apparatus to reduce the residual moisture content of the treatedmaterial to 70% or under in place of the squeeze rolls is notparticularly recommended, although fairly satisfactory results may be soobtained, since the same measure of control cannot be obtained and thesame measure of uniformity or consistency in results has not beenobtained.

As an example of the method of treatment, the following is given as atypical example of treating yarnor; thread. It is preferred that suchmaterial should be treated in the warp form rather than in the form oflarge keins.

One pound of cotton yarn or thread is boiled for ten minutes atatmospheric pressure in 4 litres of 64 grams of sodium hydroxide perlitre. The material is then washed thoroughly with hot water until it issubstantially free of alkali and is then cooled by washing incold'water.

The material is then run through squeeze rolls of the type described,which are set to retain approximately 50% of the residual moisture tothe dry weight of the material. The thread or yarn is then saturated inan acid bath comprising 38 gram of sulphuric acid per litre. Thematerial is then again passed through squeeze rolls set to obtain thelow moisture content described. This action is repeated until thematerial has been saturated in the dilute acid bath six times and hasbeen squeezed after each bath. The material is then washed in wateruntil free of acid, and dried.

What we claim is:

1. The method of treating natural cellulosic textile materials,comprising treating said materials in a hot, caustic alkali solution,washing said material to remove said alkali solution and then treatingsaid materials in a plurality of at least four dilute baths of awater-soluble acid, said material being partially dried by mechanicalmeans to a moisture retention under 70% of the weight of the dry textilematerial before said first bath and between each succeeding bath andafter the final bath.

2. The method of treating natural cellulosic textile material,comprising immersing said material in a boiling concentrated causticalkali bath of at least 12 grams sodium hydroxide per litre, washingsaid material to remove the caustic alkali solution, and then treatingsaid material at least six times in a dilute bath of a watersolubleacid, said material being partially dried to a moisture retention'under70% of the weight of the dry textile material by mechanical means beforethe first bath, between each succeeding bath, and after the final bath.

3. The method of treating natural cellulosic textile material after ithas been kier boiled, comprising washing said material in water and thensqueezing said material to an expression under 70% moisture retentioncalculated on the I weight of the dry textile material, immersing saidmaterial in a dilute bath of a water-soluble acid, again squeezing thematerial to a moisture retention of under 70%, and repeating thesaturation of said material in the dilute water-soluble acid bath andthe squeezing action to the moisture retention specified at least threetimes.

4. In a method of treating natural cellulosic textile material, thesuccessive steps of bleaching, washing said material in water,subjecting the material to the mechanical squeezing of a character toobtain under 70% retention of the residual liquid to the dry weight ofthe cellulosic textile material, saturating said material in'a dilutebath of a water-soluble acid, then squeezing said material in the mannerabove defined to obtain under 70% retention of the residual liquid tothe dry weight of the cellulosic textile material, and repeating atleast three times the saturation of said material in the dilute acidbath and the squeezing to obtain under 70% retention of the residualliquid to the dry; weight of the cellulosic textile material.

5. The method of treating natural cellulosic textile material to improveits tensile strength and absorbency, comprising immersing said materialin a caustic solution at approximately the boiling temperature forupwardly of three min utes, washing said material to remove said causticsolution, partially drying said material by mechanically squeezing it toreduce the residual liquid to under 70% of the dry weight of thecellulosic textile material, and then thoroughly saturating saidmaterial at least six successive times in a solution of sulphuric acidcontaining from 3 to 70 grams sulphuric acid per litre, said materialbeing partially dried by squeezing it to reduce the residual liquid tounder 70% of the dry weight of the cellulosic textile material betweeneach bath and after the last bath.

6. The method of treating natural cellulosic textile materials toimprove their tensile strength and absorbency, comprising immersing saidmaterial in a hot, caustic solution of at least 12 grams caustic-material per litre for at least three minutes, washing said material toremove said caustic alkali solution, and then treatin saidmaterials in aseries of at least four dilute aqueous baths of a water-soluble acid,said materials being squeezed in a manner, to obtain a moistureretention of approximately 50% of the weight 01' the dry cellulosicmaterials, before the first bath and after each succeedingbath.

7. In 'a method of treating natural cellulosic textile materials toimprove their tensile strength and absorbency, the steps comprisingfirst pretreating in a concentrated caustic solution said material toremove impurities and then thor-,

oughly saturating said material at least six successive times in asolution of sulphuric acid containing from 3 to 70 grams sulphuric acidper litre, said materials beingsqueezed after each bath in a manner todry the material to a retention of residual liquid of approximately 50%otthe dry weight of the cellulosic textile material.

8. The method of treating natural cellulosictextile materials to improvetheir tensile strength and absorbency, comprising immersing saidmaterial in a boiling caustic solution of at least 12 grams causticmaterial per liter for at least 3 minutes, washing said material toremove caustic alkali solution therefrom, and then treating saidmaterials in a series of at least 4 dilute aqueous baths of awater-soluble acid. said materials being squeezed in a manner to obtaina moisture re-

